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Anatomy & Physiology
Lecture 13: Chapter 17
The Special Senses
Page: 549 - 589
Lecturer: Dr. Barjis
Room: P313
Phone: (718) 260-5285
E-Mail: [email protected]
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Frederic H. Martini
Fundamentals of
Learning Objectives
• Describe the sensory organs of smell, and trace
the olfactory pathways to their destination in the
brain.
• Identify the accessory and internal structures of
the eye, and explain their function.
• Explain how light stimulates the production of
nerve impulses, and trace the visual pathways to
their destination in the brain.
• Describe the structures of the external and middle
ear and explain how they function.
Learning Objectives
• Describe the parts of the inner ear and their roles
in equilibrium and hearing.
• Trace the pathways for the sensations of
equilibrium and hearing to their destinations in
the brain.
Olfaction
Olfactory organs
• Contain olfactory epithelium with olfactory
receptors, supporting cells, basal cells
• Olfactory receptors are modified neurons
• Surfaces are coated with secretions from olfactory
glands
• Olfactory reception involved detecting dissolved
chemicals as they interact with odorant binding
proteins
The Olfactory Organs
Olfaction
• Olfactory pathways
• No synapse in the thalamus for arriving
information
• Olfactory discrimination
• Can distinguish thousands of chemical stimuli
• CNS interprets smells by pattern of receptor
activity
• Olfactory receptor population shows
considerable turnover
• Number of receptors declines with age
Gustation
Taste receptors
• Clustered in taste buds
• Associated with lingual papillae
Taste buds
• Contain basal cells which appear to be stem cells
• Gustatory cells extend taste hairs through a
narrow taste pore
Gustatory Reception
Gustatory pathways
• Taste buds are monitored by cranial nerves
• Synapse within the solitary nucleus of the
medulla oblongata
• Then on to the thalamus and the primary
sensory cortex
Gustatory discrimination
• Primary taste sensations
• Sweet, sour, salty, bitter
• Receptors also exist for umami and water
• Taste sensitivity shows significant individual
differences, some of which are inherited
• The number of taste buds declines with age
Vision
Accessory structures of the eye
• Eyelids (palpebrae) separated by the
palpebral fissue
• Eyelashes
• Tarsal glands
• Lacrimal apparatus
Eternal Features and Accessory Structures of the
Eye
external structures of the eye
• Conjunctiva covers most of eye
• Cornea is transparent anterior portion
Lacrimal apparatus
• Secretions from the lacrimal gland contain
lysozyme
• Tears form in the lacrimal glands, wash across
the eye and collect in the lacrimal lake
• Pass through the lacrimal punctae, lacrimal
canaliculi, lacrimal sac and nasolacrimal duct
The eye
• Three layers
• Outer fibrous tunic
• Sclera, cornea, limbus
• Middle vascular tunic
• Iris, ciliary body, choroid
• Inner nervous tunic
• Retina
The Sectional Anatomy of the Eye
internal structures of the eye
• Ciliary body
• Ciliary muscles and ciliary processes, which
attach to suspensory ligaments of lens
• Retina
• Outer pigmented portion
• Inner neural part
• Rods and cones
The Sectional Anatomy of the Eye
The Pupillary Muscles
retina
• Retina contains rods and cones
• Cones densely packed at fovea (center of the
macula lutea)
• Retinal pathway
• Photoreceptors to bipolar cells to ganglion
cells, to the brain via the optic nerve
• Axons of ganglion cells converge at blind
spot (optic disc)
• Horizontal cells and amacrine cells modify the
signal passed along the retinal neurons
The Organization of the Retina
The Organization of the Retina
Eye anatomy
• Ciliary body and lens divide the anterior cavity of
the eye into posterior (vitreous) cavity and
anterior cavity
• Anterior cavity further divided
• anterior chamber in front of eye
• posterior chamber between the iris and the
lens
The Circulation of Aqueous Humor
Fluids in the eye
• Aqueous humor circulates within the eye
• diffuses through the walls of anterior chamber
• passes through canal of Schlemm
• re-enters circulation
• Vitreous humor fills the posterior cavity.
• Not recycled – permanent fluid
Lens
• Posterior to the cornea and forms anterior
boundary of posterior cavity
• Posterior cavity contains vitreous humor
• Lens helps focus
• Light is refracted as it passes through lens
• Accommodation is the process by which the
lens adjusts to focus images
• Normal visual acuity is 20/20
Image Formation
Accommodation
Figure 17.10
Visual Abnormalities
Visual physiology
• Rods – respond to almost any photon
• Cones – specific ranges of specificity
Rods and Cones
Photoreceptor structure
• Outer segment with membranous discs
• Narrow stalk connecting outer segment to inner
segment
• Light absorption occurs in the visual pigments
• Derivatives of rhodopsin
Photoreception
Animation: Photoreception (see tutorial)
Photoreception
Bleaching and Regeneration of Visual Pigments
Color sensitivity
• Integration of information from red, blue and
green cones
• Colorblindness is the inability to detect certain
colors
retinal adaptation
• Dark adapted – most visual pigments are fully
receptive to stimulation
• Light adapted – pupil constricts and pigments
bleached.
the visual pathway
• Large M-cells monitor rods
• Smaller more numerous P cells monitor cones
Convergence and Ganglion Cell Function
Seeing in stereo
• Vision from the field of view transfers from one
side to the other while in transit
• Depth perception is obtained by comparing
relative positions of objects from the two eyes
The Visual Pathways
Visual circadian rhythm
• Input to suprachiasmic nucleus affects the
function of the brainstem
• Circadian rhythm ties to day-night cycle, and
affects metabolic rates
Equilibrium and Hearing
Both equilibrium and hearing are provided by
receptors of the inner ear
Anatomy of the ear – External Ear
• Auricle or pinnae surrounds the ear
• External acoustic meatus ends on tympanic
membrane
The Anatomy of the Ear
Middle ear
• Communicates with pharynx via
pharyngotympanic membrane
• Middle ear encloses and protects the auditory
ossicles
The Middle Ear
Inner ear
• Membranous labyrinth contains endolymph
• Bony labyrinth surrounds and protects
membranous labyrinth
• Vestibule
• Semicircular canals
• Cochlea
The Inner Ear
Figure 17.22
Components of the inner ear
• Vestibule contains the utricle and saccule
• Semicircular canals contain the semicircular
ducts
• Cochlea contains the cochlear duct
Windows
• Round window separates the perilymph from the
air spaces of the middle ear
• Oval window connected to the base of the stapes
• Basic receptors of inner ear are hair cells
• Provide information about the direction and
strength of stimuli
Equilibrium
• Anterior, posterior and lateral semicircular ducts
are continuous with the utricle
• Each duct contains an ampulla with a
gelatinous cupula and associated sensory
receptor
• Saccule and utricle connected by a passageway
continuous with the endolymphatic duct
• Terminates in the endolymphatic sac
• Saccule and utricle have hair cells clustered in
maculae
• Cilia contact the otolith (statoconia)
The Vestibular Complex
The Vestibular Complex
The Vestibular Complex
Vestibular neural pathway
• Vestibular receptors activate sensory neurons of
the vestibular ganglia
• Axons form the vestibular branch of cranial nerve
VII
• Synapses within the vestibular nuclei
Pathways for Equilibrium Sensation
Hearing
• Cochlear duct lies between the vestibular duct
and the tympanic duct
• Hair cells of the cochlear duct lie within the
Organ of Corti
• Intensity is the energy content of a sound
• Measured in decibels
The Cochlea
The Organ Of Corti
Pathway of sound
• Sound waves travel toward tympanic membrane,
which vibrates
• Auditory ossicles conduct the vibration into the
inner ear
• Tensor tympani and stapedius muscles contract
to reduce the amount of movement when loud
sounds arrive
• Movement at the oval window applies pressure to
the perilymph of the cochlear duct
• Pressure waves distort basilar membrane
• Hair cells of the Organ of Corti are pushed against
the tectoral membrane
Sound and Hearing
Sound and Hearing
Neural pathway
• Sensory neurons of hearing are located in the
spiral ganglion of the cochlea
• Afferent fibers form the cochlear branch of
cranial nerve VIII
• Synapse at the cochlear nucleus
You should now be familiar with:
• The sensory organs of smell, and the olfactory
pathways in the brain.
• The accessory and internal structures of the eye,
and their functions.
• How light stimulates the production of nerve
impulses, and the visual pathways.
• The structures of the external and middle ear and
how they function.
• The parts of the inner ear and their roles in
equilibrium and hearing.
• The pathways for the sensations of equilibrium and
hearing.